LI-COR Environmental NewsLine

Avoid ‘mass’ confusion with the LI-6400XT

Gas exchange from the surface of a leaf is typically reported in micromoles of CO₂ exchanged per square meter of substrate per second, abbreviated as µmol m^-2 s^-1. However, users may want to express gas exchange rates on a mass basis, such as µmol kg^-1 s^-1. The LI-6400XT Portable Photosynthesis System can perform these calculations for you, while measurements are ongoing or after data are collected during post-processing.

To express gas exchange rates on a mass basis during the measurement, simply enter your leaf mass in place of leaf area in the LI-6400XT software. To avoid later unit conversions, enter the mass in decigrams rather than grams*. Note that only photosynthesis and transpiration measurements remain valid when using this correction.

In the example , 4 g of leaf tissue is entered as 40 decigrams (even though the units are displayed as cm²) . The LI-6400XT calculates the rate based on the entered mass; no post-processing is required.

Alternatively, after the data are collected, the mass can be entered to correct the calculated rates using the Excel file generated by the LI-6400XT (shown below).

* This is because we convert from cm² leaf area to m² leaf area, which is 100 x 100, or 10⁴.  See Chapter 1 of ‘Using the LI-6400/LI-6400XT’ for more details.

Tags: LI-6400XT, Photosynthesis

This article was originally posted on Wednesday, April 13th, 2011.